1. Field of the Invention
The invention relates to a blade for a gas turbine and, in particular, to cooling for the shroud of the blade.
2. Brief Description of the Related Art
Shrouds for gas turbine blades serve for sealing and limiting the leakage flow in the gap region between the blade tips and the radially opposite stator or rotor. Such shrouds extend in the circumferential direction and, over a defined region, in the direction of the turbine axis, as far as possible so as to match the contour of the inner housing or of the rotor. For the purpose of improving the sealing, conventional shrouds in many instances also have one or more sealing ribs, also called fins, which run from a platform of the shroud, that is to say of an essentially flat portion of the shroud, along the radial direction.
For the purpose of prolonging their operating time in the gas turbine through which hot gas flows, the shrouds are cooled convectively, as disclosed, for example, in EP 1013884 and EP 1083299. These documents each describe a blade with a shroud which has a plurality of bores for a cooling air flow. The bores are connected to a cooling duct in the blade leaf and each lead to a lateral exit in the circumferential direction.
EP 1041247 discloses a gas turbine blade with inner radially cooling ducts which issue into a plenum 42 and 44. Bores 54, 56, 58 extend from there in the plane of the shroud, the shroud being cooled by means of film and convective cooling through the bores. In a variant, the bores extend from the plenum obliquely and in a slightly radial direction with respect to the radially outer surface of the shroud platform.
A shroud of a gas turbine blade is subjected to varying thermal load along the direction of flow of the hot gas and also, in various regions, to varying mechanical load. Consequently, the requirements for cooling and mechanical load-bearing capacity in various regions of the shroud are also different. This is taken into account, in the aforementioned gas turbine blades, by the matching of the bore diameters and other measures for changing the pressure differentials.